X-ray imaging system with a combined filter and collimator positioning mechanism

ABSTRACT

A radiation therapy system includes an X-ray imaging system that is configured with a combined and simplified filter and collimator positioning mechanism. In addition, an X-ray imager of the RT system is only positioned at a few discrete locations within a plane that is a fixed distance from the imaging X-ray source when generating X-ray images. As a result, for each of these discrete imaging positions, the simplified filter and collimator positioning mechanism positions a specific collimator-filter combination in a specific location between the X-ray source and the imager.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation under 35 U.S.C. § 120 of U.S.patent application Ser. No. 15/935,042, filed Mar. 25, 2018, whichclaims the benefit of U.S. Provisional Application No. 62/566,301, filedSep. 29, 2017. The aforementioned U.S. Patent Application and U.S.Provisional Application, including any appendices or attachmentsthereof, are hereby incorporated by reference in their entirety.

BACKGROUND

Unless otherwise indicated herein, the approaches described in thissection are not prior art to the claims in this application and are notadmitted to be prior art by inclusion in this section.

Radiation therapy, which is the use of ionizing radiation, is alocalized treatment for a specific target tissue, such as a canceroustumor. Ideally, radiation therapy is performed on target tissue (alsoreferred to as the planning target volume) that spares the surroundingnormal tissue from receiving doses above specified tolerances, therebyminimizing risk of damage to healthy tissue. Prior to the delivery ofradiation therapy, an imaging system is typically employed to provide athree dimensional image of the target tissue and surrounding area. Fromsuch imaging, the size and mass of the target tissue can be estimatedand an appropriate treatment plan generated and target volumedetermined.

So that the prescribed dose is correctly supplied to the planning targetvolume during radiation therapy, the patient should be correctlypositioned relative to the linear accelerator that provides theradiation therapy. Typically, patient geometric data is checked beforeand during the treatment, to ensure correct patient placement. Thisprocess is referred to as image guided radiation therapy (IGRT), andinvolves the use of an imaging system to view target tissues whileradiation treatment is delivered to the planning target volume. IGRTincorporates imaging coordinates from the treatment plan to ensure thepatient is properly aligned for treatment in the radiation therapydevice.

One challenge of radiation therapy is generating sufficiently clearimages of the planning target volume using the lowest possible imagingdose. To that end, RT systems commonly include shaped filters, referredto as “bow-tie” filters, which are in the path of an imaging beam andmaintain a more uniform distribution of X-ray photons across the fieldof view. Furthermore, to limit the size and shape of an imaging beam,and to limit X-ray scatter that can degrade image quality, a collimatoris also typically positioned in the path of the imaging beam. However,correctly positioning a bow-tie filter and a collimator in an RT systemcan be a complex problem. This is because, for a given position of theimager, both the collimator and bow-tie filter must be precisely andindependently positioned relative to the imager and to each other inorder to properly shape the imaging beam. Further, to maximizeflexibility in image acquisition positions, RT systems typically includean imager for receiving imaging X-rays that can be positioned withmultiple degrees of freedom about a patient. Thus, such RT systemsinclude a complex imaging collimation system with multiple (typicallyfour) completely independent collimator blades for shaping the imagingbeam. Adding further mechanical and control complexity, such RT systemgenerally also includes an independent movement system for positioningthe bow-tie filter.

In light of the above, there is a need in the art for radiation therapysystems that address the above-described challenges.

BRIEF DESCRIPTION OF THE DRAWINGS

Features of the present disclosure will become more fully apparent fromthe following description and appended claims, taken in conjunction withthe accompanying drawings. These drawings depict only severalembodiments in accordance with the disclosure and are, therefore, not tobe considered limiting of its scope. The disclosure will be describedwith additional specificity and detail through use of the accompanyingdrawings.

FIG. 1 illustrates a clinical environment in which an embodiment of thepresent disclosure can be integrated.

FIG. 2 schematically illustrates a front view of an RT treatment system,according to various embodiments of the present disclosure.

FIGS. 3A, 3B, and 3C schematically illustrate an X-ray imager whenpositioned for generating images in a center imaging position and in alateral offset position, according to various embodiments of the presentdisclosure.

FIG. 4 schematically illustrates components of RT treatment systemconfigured to generate planar images and/or live-images of a patient,according to an embodiment of the present disclosure.

FIG. 5 schematically illustrates components of an RT treatment systemconfigured to enable CBCT imaging of a head or other localized portionof a patient, according to an embodiment of the present disclosure.

FIG. 6 schematically illustrates components of an RT treatment systemconfigured to enable half-fan CBCT imaging of a thorax or other largeregion of a patient, according to an embodiment of the presentdisclosure.

FIG. 7 is a schematic view from an X-ray imager in an RT treatmentsystem of a positioning mechanism, a first combined filter-collimatorassembly, a second combined filter-collimator assembly, and afilter-free collimator, according to an embodiment of the presentdisclosure.

FIG. 8 is a schematic view from an X-ray imager in an RT treatmentsystem of a positioning mechanism, a first combined filter-collimatorassembly, a second combined filter-collimator assembly, and afilter-free collimator, according to an embodiment of the presentdisclosure.

FIG. 9 sets forth a flowchart summarizing an example method forgenerating an X-ray image, according to one or more embodiments of thepresent disclosure.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof. In the drawings,similar symbols typically identify similar components, unless contextdictates otherwise. The illustrative embodiments described in thedetailed description, drawings, and claims are not meant to be limiting.Other embodiments may be utilized, and other changes may be made,without departing from the spirit or scope of the subject matterpresented here. It will be readily understood that the aspects of thedisclosure, as generally described herein, and illustrated in thefigures, can be arranged, substituted, combined, and designed in a widevariety of different configurations, all of which are explicitlycontemplated and make part of this disclosure.

As noted above, when radiation treatment (RT) treatment is appliedaccurately to targeted tissue in a patient, there is minimal impact onhealthy tissue surrounding the targeted tissue. However, the positioningof the collimator and filter for the imaging system included in RTsystems is necessarily complex, including a movement system for multipleindependently positioned collimator blades (to adjust the imaging field)and another movement system for an independently positioned bow-tiefilter (to provide a field of view that receives a uniform distributionof X-ray photons). According to various embodiments, an RT systemincludes an X-ray imaging system that is configured with a combined andsimplified filter and collimator positioning mechanism. In addition, insome embodiments, an X-ray imager of the RT system is only positioned ata few discrete locations within a plane that is a fixed distance fromthe imaging X-ray source when generating X-ray images. As a result, foreach of these discrete imaging positions, the positioning mechanismpositions a specific collimator-filter combination in a specificlocation between the X-ray source and the imager. That is, for each ofthe discrete locations at which the imager is positioned for generatingimages, the positioning mechanism implements a single correspondingcollimator-filter configuration. Thus, the complex systems usuallyemployed for precisely changing the position the collimator and thefilter in real time are not needed.

FIG. 1 illustrates a clinical environment 100 in which an embodiment ofthe present disclosure can be integrated. Clinical environment 100includes a radiotherapy (RT) treatment room 120 with an RT treatmentsystem 110 disposed therein and a control room 130, separated by ashielded wall 101. RT treatment system 110 includes a linear accelerator(LINAC) 121 that generates a megavolt (MV) treatment beam 122 of highenergy X-rays (or in some embodiments electrons), a patient table orcouch 123, a kilovolt (kV) X-ray source 124, an X-ray imager 150, and,in some embodiments, an MV electronic portal imaging device (EPID) 125.Control room 130 includes an image acquisition and treatment controlcomputer 131 communicatively coupled to X-ray imager 150 via anacquisition cable 102, and an associated control console 132.

Also shown in FIG. 1 is a patient 160, positioned on couch 123 for RTtreatment. Patient 160 includes a target region 161. Target region 161may be, for example, a tumor to receive RT treatment, and can be locatedin different regions of the body of patient 160, such as the head,thorax, or leg. Different regions of the human body each have adifferent cross-sectional profile. For example, the head is generallyround in cross-section whereas the torso is typically thicker laterallythan vertically. Consequently, to create a more uniform imaging beamintensity across the surface of X-ray imager 150, a differentcompensating filter is typically employed during imaging, depending onthe region of the body being imaged. The correct compensating filter canappropriately reduce the imaging beam intensity at the periphery of thebeam. Thus, the imaging system included in RT treatment system 110typically includes two or more compensating filters (not shown in FIG.1), which are described in greater detail below in conjunction withFIGS. 5 and 6.

LINAC 121 customizes a treatment beam 122 to conform to the shape of atumor in target region 161 of patient 160. Thus, LINAC 121 destroyscancer cells while sparing surrounding normal tissue when the locationof target region 161 is precisely known. KV X-ray source 124 is an X-raysource for generating an imaging beam 126, which is directed towardX-ray imager 150 for imaging target region 161 and surrounding areasduring RT treatment. For example, in some embodiments, clinicalenvironment 100 is employed for image-guided radiation therapy (IGRT),which uses image guidance procedures for target localization before andduring treatment. In such embodiments, the images used to preciselymonitor the current location of target region 161 are generated with kVX-ray source 124 and X-ray imager 150. Alternatively or additionally, insome embodiments, images generated with kV X-ray source 124 and X-rayimager 150 can be employed in intensity-modulated radiation therapy(IMRT) applications. In either IGRT or IMRT applications, elements of RTtreatment system 110 rotate about couch 123 during RT treatment. Forexample, in some embodiments, LINAC 121, EPID 125, kV X-ray source 124,and X-ray imager 150 rotate about couch 123 as indicated. One embodimentof RT treatment system 110 is described below in conjunction with FIG.2.

FIG. 2 schematically illustrates a front view of RT treatment system110, according to various embodiments of the present disclosure. In FIG.2, elements of RT treatment system 110 (LINAC 121, EPID 125, a treatmentbeam collimator 210, kV X-ray source 124, and X-ray imager 150) areshown partially rotated about couch 123 at a specific point in timeduring operation. In the embodiment illustrated in FIG. 2, kV X-raysource 124 and X-ray imager 150 are shown at a 45° rotation positionwhile LINAC 121 and EPID 125 are shown in FIG. 2 at the corresponding135° rotation position.

LINAC 121 (which generates treatment beam 122), EPID 125, a treatmentbeam collimator 210, kV X-ray source 124, and X-ray imager 150 rotateabout a center point of rotation 201, which is disposed along an X-raypath 202 from kV X-ray source 124 to a point on an X-ray detectionsurface (not shown) of X-ray imager 150. For example, in someembodiments, X-ray path 202 is a shortest path from kV X-ray source 124to a point on an X-ray detection surface (not shown) of X-ray imager150. Generally, X-ray path 202 has a length L and is the path from kVX-ray source 124 to a center point of X-ray imager 150 when X-ray imager150 is located at a center imaging position, thereby defining a verticaldirection 203 between kV X-ray source 124 and X-ray imager 150. In acenter imaging position, which is shown in FIG. 2, X-ray imager 150 issubstantially centered on X-ray path 202. By contrast, in a lateraloffset position (indicated by dashed lines), an edge 151 and/or an edgeportion 152 of X-ray imager 150 is a distance along X-ray path 202 fromkV X-ray source 124 that is equal to length L. In either the centerimaging position or the lateral offset position, at least a portion ofX-ray imager 150 is a fixed rotational distance R along X-ray path 202from center point of rotation 201. In some embodiments, RT treatmentsystem 110 is configured to generate X-ray images with X-ray imager 150in at least the center imaging position and the lateral offset position,as appropriate for a particular imaging application. Examples of thepositioning of X-ray imager 150 for various imaging applications areillustrated in FIGS. 3A, 3B, and 3C.

FIGS. 3A, 3B, and 3C schematically illustrate X-ray imager 150 whenpositioned for generating images in a center imaging position and in alateral offset position, according to various embodiments of the presentdisclosure. Specifically, FIG. 3A illustrates a view of X-ray imager 150from kV X-ray source 124 when X-ray imager 150 and couch 123 arepositioned for generating X-ray images of the thorax 301 of patient 160.FIG. 3B illustrates a view of X-ray imager 150 from kV X-ray source 124when X-ray imager 150 and couch 123 are positioned for generating X-rayimages of the head 302 of patient 160. FIG. 3C illustrates a view ofX-ray imager 150 from kV X-ray source 124 when X-ray imager 150 andcouch 123 are positioned for generating X-ray images of thorax 301 ofpatient 160 in half-fan cone-beam computed tomography (CBCT) mode. Inmany applications, X-ray imager 150 and kV X-ray source 124 (not shownin FIGS. 3A, 3B, and 3C) rotate about couch 123. Therefore, in suchapplications, X-ray imager 150 and kV X-ray source 124 are not fixed inposition relative to couch 123. Thus, for reference, couch 123 and X-rayimager 150 are shown in FIGS. 3A, 3B, and 3C at a point in time when kVX-ray source 124 has rotated to a position directly above couch 123 andX-ray imager 150 is rotated to a position below couch 123. That is, kVX-ray source 124 and X-ray imager 150 are shown in FIGS. 3A, 3B, and 3Cat a 0° rotation position.

In FIG. 3A, X-ray imager 150 is positioned in a center imaging positionto enable X-ray imaging of thorax 301 of patient 160. Therefore, when kVX-ray source 124 is rotated to a position directly above couch 123,X-ray imager 150 is positioned directly below couch 123 and is centeredin lateral direction 311 on a longitudinal axis 303 of couch 123. Thatis, a center point 153 of an X-ray detection surface of X-ray imager 150is disposed on or proximate X-ray path 202. It is noted that in someembodiments, X-ray imager 150 and couch 123 are positioned in the centerimaging position as shown for generating either planar images,live-imaging, or full-fan CBCT images of thorax 301 of patient 160.

In FIG. 3B, X-ray imager 150 is positioned in a center imaging positionto enable X-ray imaging of head 302 of patient 160. Therefore, when kVX-ray source 124 is rotated to a position directly above couch 123,X-ray imager 150 is positioned directly below couch 123 and is centeredin lateral direction 311 on longitudinal axis 303 of couch 123. Todirect imaging beam 126 (not shown in FIG. 3B) to head 302, couch 123 istranslated in a longitudinal direction 312 relative to X-ray imager 150.It is noted that in some embodiments, X-ray imager 150 and couch 123 arepositioned in the center imaging position shown in FIG. 3B forgenerating either planar images or full-fan CBCT images of head 302 ofpatient 160. In embodiments in which full-fan CBCT image of head 302 aregenerated, a specific shaping filter (not shown) is typically employedto generate a more uniform intensity of imaging beam 126 across X-rayimager 150, as described in greater detail below. By contrast, inembodiments in which planar (2D) images and/or live images aregenerated, a shaping filter is generally not employed.

In FIG. 3C, X-ray imager 150 is positioned in a lateral offset positionto enable half-fan CBCT X-ray imaging of thorax 301 of patient 160. Inhalf-fan CBCT X-ray imaging, only half of thorax 302 is irradiated withimaging beam 126 (not shown in FIG. 3C) for each projection generated aspart of the volumetric data set for the CBCT imaging process. Therefore,when kV X-ray source 124 is rotated to a position directly above couch123, X-ray imager 150 is positioned to be displaced from the centerimaging position in lateral direction 311, which is a directionperpendicular to X-ray path 202 (shown in FIG. 2). In some embodiments,when X-ray imager 150 is in the lateral offset position, X-ray imager150 is positioned so that edge 151 of X-ray imager 150 is substantiallyaligned with longitudinal axis 303. Alternatively, in some embodiments,when X-ray imager 150 is in the lateral offset position, X-ray imager150 is positioned so that edge portion 152 of X-ray imager 150 issubstantially aligned with longitudinal axis 303. It is noted that insome embodiments, X-ray imager 150 and couch 123 are positioned in thelateral offset imaging position shown in FIG. 3C for generating half-fanCBCT images of thorax 301 of patient 160. In such embodiments, aspecific compensating filter (not shown) is typically employed togenerate a more uniform intensity of imaging beam 126 across X-rayimager 150, as described in greater detail below. The compensatingfilter employed in the lateral offset position is generally a differentfilter than the compensating filter employed in the center imagingposition.

Returning to FIG. 2, RT treatment system 110 also includes a positioningmechanism 220, a first combined filter-collimator assembly 230, a secondcombined filter-collimator assembly 240, and a filter-free collimator250. According to various embodiments of the present disclosure,positioning mechanism 220 is disposed between kV X-ray source 124 andX-ray imager 150, and is configured to selectively position one of firstcombined filter-collimator assembly 230, second combinedfilter-collimator assembly 240, or filter-free collimator 250 alongX-ray path 202. Thus, when X-ray imager 150 is in the center imagingposition for generating planar X-ray images of patient 160, positioningmechanism 220 can be employed to position filter-free collimator 250along X-ray path 202; when X-ray imager 150 is in the center imagingposition for generating full-fan CBCT images of patient 160, positioningmechanism 220 can be employed to position first combinedfilter-collimator assembly 230 along X-ray path 202; and when X-rayimager 150 is in the lateral offset imaging position for generatinghalf-fan CBCT images of patient 160, positioning mechanism 220 can beemployed to position second combined filter-collimator assembly 240along X-ray path 202.

Positioning mechanism 220 can include any suitable mechanism operable toselectively position one of first combined filter-collimator assembly230, second combined filter-collimator assembly 240, or filter-freecollimator 250 along X-ray path 202. For example, in some embodiments,positioning mechanism 220 includes a slider mechanism that is motorizedand has a simple 2-channel position detection system, such as a steppermotor. Various embodiments of positioning mechanism 220 are described ingreater detail below in conjunction with FIGS. 7 and 8.

Generally, RT treatment system 110 includes multiple combinedfilter-collimator assemblies. Each such combined filter-collimatorassembly includes a different compensating filter, and each compensatingfilter is configured to generate uniform imaging beam intensity 126across X-ray imager 150 for a different imaging position and/orapplication of X-ray imager 150. Thus, in the embodiment illustrated inFIG. 2, RT treatment system 110 includes two combined filter-collimatorassemblies—one for each imaging position of X-ray imager 150. In otherembodiments, RT treatment system 110 includes more than two or only asingle combined filter-collimator assembly. In such embodiments, eachcombined filter-collimator assembly is configured to suitably modifyimaging beam 126 for a different imaging position of X-ray imager 150relative to X-ray path 202, and typically includes a compensating filterthat is unique from other compensating filters included in the othercombined filter-collimator assemblies of RT treatment system 110.

X-ray imager 150 generates images from a small number of discretelocations, two possible examples of which are illustrated in FIG. 2.According to various embodiments of the present disclosure, thesediscrete imaging locations for X-ray imager 150 vary in a singledirection relative to kV X-ray source 124. Specifically, the discreteimaging locations for X-ray imager 150 are disposed in a plane that isperpendicular to X-ray path 202. For example, in the embodimentillustrated in FIG. 2, X-ray imager 150 is fixed relative to kV X-raysource 124 longitudinally, i.e., in longitudinal direction 312 shown inFIG. 3, which is the direction directly out of the page in FIG. 2. Thus,at each imaging position, X-ray imager 150 is disposed in a plane thatincludes kV X-ray source 124 and each of the other imaging positions ofX-ray imager 150. In addition, in the embodiment illustrated in FIG. 2,X-ray imager 150 is fixed relative to kV X-ray source 124 in verticaldirection 203, i.e., in the direction parallel to X-ray path 202. Thus,at each imaging position, a portion of X-ray imager 150 is disposedalong X-ray path at a distance L from kV X-ray source 124.

In sum, RT treatment system 110 includes a simplified imaging systemthat can be used for the most common treatments and imaging positions,but not for all possible treatments. For treatment cases that rely onthe imaging positions for which RT treatment system 110 is configured,RT treatment system 110 can employ state-of-the-art technology,including IMRT, IGRT, and the like, but without the drawbacks inherentin more complex systems. Specifically, in place of reduced flexibility,RT system 110 includes vertically and laterally fixed imager positions(described above), and a simplified kV collimation system. For example,the most common uses of the collimation/filter system for RT imagingsystems employ the collimator in the center imaging position and thelateral offset (half-fan CBCT) imaging position. Thus, having X-rayimager 150 fixed in vertical direction 203 and longitudinal direction312 does not affect imaging, but greatly simplifies the kVcollimation/filter system. Having no adjustability in the longitudinalfield size allows for fixed collimation in that direction. For eachimaging position in the lateral direction, a suitable fixed compensatingfilter can be implemented with positioning mechanism 220 as appropriate,such as a bow-tie filter. Examples of various imaging positions and thepositioning of suitable compensating filters and lateral collimation viapositioning mechanism 220 are described below in conjunction with FIGS.4-6.

FIG. 4 schematically illustrates components of RT treatment system 110configured to generate planar images and/or live-images of patient 160,according to an embodiment of the present disclosure. Specifically,X-ray imager 150 and couch 123 are in the center imaging positionillustrated in FIG. 3A, and positioning mechanism 220 has selectivelypositioned filter-free collimator 250 along X-ray path 202. Thus, kVX-ray source 124 is rotated to a position directly above couch 123, andX-ray imager 150 is positioned directly below couch 123 and is centeredin lateral direction 311 on X-ray path 202 and on longitudinal axis 303of couch 123. Since X-ray imager 150 is used to generate planar imagesand/or live-images of patient 160 in the embodiment illustrated in FIG.4, kV X-ray source 124 and X-ray imager 150 are generally staticrelative to patient 160 at any selected rotation angle around therotation center 201.

Filter-free collimator 250 is configured to limit the extent of X-rayexposure in lateral direction 311 of patient 160 and of X-ray imager150. For example, in some embodiments, filter-free collimator 250includes two blades 401 with an opening 402 therebetween that is sizedto enable imaging beam 126 to reach most or all of the detector surfaceof X-ray imager 150 as shown. In some embodiments, blades 401 eachinclude a plate of lead, tungsten, or any other suitable material forabsorbing incident X-rays. Generally, opening 402 is fixed.

In some embodiments, RT treatment system 110 further includes alongitudinal collimator 410 that limits the extent of X-ray exposure inlongitudinal direction 312, which in FIG. 4 is directly out of the page.In such embodiments, longitudinal collimator 410 can include two blades411 with an opening (not visible in FIG. 4) therebetween that is sizedto enable imaging beam 126 to reach most or all of the detector surfaceof X-ray imager 150 in longitudinal direction 312 (which is out of pagein FIG. 4). Thus, together longitudinal collimator 410 and filter-freecollimator 250 define the rectangular region of X-ray imager 150 andpatient 160 that is exposed to imaging beam 126. Blades 411 can eachinclude a plate formed from similar materials as described above forblades 401.

FIG. 5 schematically illustrates components of RT treatment system 110configured to enable CBCT imaging of head 302 or other localized portionof patient 160, according to an embodiment of the present disclosure.Specifically, X-ray imager 150 and couch 123 are in the center imagingposition illustrated in FIG. 3B, and positioning mechanism 220 hasselectively positioned first combined filter-collimator assembly 230along X-ray path 202. Typically, positioning mechanism 220 positionsfirst combined filter-collimator assembly 230 in X-ray path 202 betweenlongitudinal collimator 410 and X-ray imager 150.

KV X-ray source 124 and X-ray imager 150 rotate about center point ofrotation 201 and are therefore not fixed in position relative to couch123. FIG. 5 depicts RT treatment system 110 when kV X-ray source 124 isrotated to a position directly above couch 123 and X-ray imager 150 ispositioned directly below couch 123. As shown, at such a point in time,X-ray imager 150 is centered in lateral direction 311 on X-ray path 202and on longitudinal axis 303 of couch 123.

First combined filter-collimator assembly 230 includes a collimator 510,a compensating filter 520, and, in some embodiments, an intensity filter530. Collimator 510 is configured to limit the extent of X-ray exposurein lateral direction 311 of patient 160 and to align incident imagingbeam 126 with X-ray imager 150. For example, in some embodiments,collimator 510 includes two blades 501 with an opening 502 therebetweenthat is sized to enable imaging beam 126 to reach most or all of thedetector surface of X-ray imager 150 as shown. Blades 501 can eachinclude a plate formed from similar materials as described above forblades 401. Generally, opening 502 is fixed. Compensating filter 520 isconfigured to create a more uniform intensity of imaging beam 126 acrossthe surface of X-ray imager 150 when X-ray imager 150 is in the centerimaging position. Compensating filter 520 can be, for example, a bowtiefilter, and in some embodiments, can be formed from aluminum.

Intensity filter 530 is configured to provide additional X-rayfiltering, and is typically a uniform plate of X-ray absorbing material,such as titanium. In some embodiments, intensity filter 530 isphysically coupled to or mounted on first combined filter-collimatorassembly 230, and therefore is moved together with first combinedfilter-collimator assembly 230 by positioning mechanism 220.Alternatively, intensity filter 530 can be moved into position in X-raypath 202 separately from first combined filter-collimator assembly 230.Similarly, in some embodiments, collimator 510 is physically coupled toor mounted on compensating filter 520, and therefore is moved togetherwith compensating filter 520 as a single assembly by positioningmechanism 220. Alternatively, collimator 510 can be moved into positionin X-ray path 202 separately from compensating filter 520. Together,longitudinal collimator 410 and collimator 510 define the rectangularregion of X-ray imager 150 and patient 160 that is exposed to imagingbeam 126.

As noted above, during operation X-ray imager 150 is fixed in verticaldirection 203 relative to kV X-ray source 124. As a result, from a fixedlocation in vertical direction 203 relative to kV X-ray source 124 andX-ray imager 150, collimator 510 correctly limits the extent of imagingbeam 126 in lateral direction 311. That is, real-time variation of theposition of collimator 510 in vertical direction 203 is not necessary.Similarly, from a fixed location in vertical direction 203 relative tokV X-ray source 124 and X-ray imager 150, compensating filter 520 cancorrectly equalize or balance the intensity of imaging beam 126 thatreaches X-ray imager 150, and real-time variation of the position ofcompensating filter 520 in vertical direction 203 is not necessary.Thus, X-ray imager 150 can generate state-of-the-art X-ray images andvolumetric data sets without the complex positioning mechanism employedin conventional RT systems. For example, in the embodiment illustratedin FIG. 5, collimator 510 is positioned a fixed vertical distance L2from X-ray imager 150 and a fixed vertical distance L3 from kV X-raysource 124. That is, during imaging, vertical distance L2 (betweencollimator 510 and X-ray imager 150) and vertical distance L3 (betweencollimator 510 and kV X-ray source 124) each remain constant. Similarly,compensating filter 520 is positioned a fixed vertical distance L4 fromX-ray imager 150 and a fixed vertical distance L5 from kV X-ray source124. Consequently, during imaging, vertical distance L4 (betweencompensating filter 520 and X-ray imager 150) and vertical distance L5(between compensating filter 520 and kV X-ray source 124) each remainconstant.

It is noted that for each other imaging position of X-ray imager 150,positioning mechanism 220 is configured to position a different combinedfilter-collimator assembly in X-ray path 202. Second combinedfilter-collimator assembly 240 is just one such example. Each differentcombined filter-collimator assembly includes a different configurationof compensating filter than compensating filter 520 and a differentcollimator than collimator 510. Also, in each different combinedfilter-collimator assembly, the vertical distances between thecompensating filter, collimator, X-ray imager 150, and kV X-ray source124 can be different than vertical distances L2, L3, L4, and L5.

FIG. 6 schematically illustrates components of RT treatment system 110configured to enable half-fan CBCT imaging of thorax 301 or other largeregion of patient 160, according to an embodiment of the presentdisclosure. Specifically, X-ray imager 150 is in the lateral offsetimaging position illustrated in FIG. 3C, and positioning mechanism 220has selectively positioned second combined filter-collimator assembly240 along X-ray path 202. Typically, positioning mechanism 220 positionssecond combined filter-collimator assembly 240 in X-ray path 202 betweenlongitudinal collimator 410 and X-ray imager 150.

In FIG. 6, KV X-ray source 124 and X-ray imager 150 rotate about centerpoint of rotation 201 and are therefore not fixed in position relativeto couch 123. FIG. 6 depicts RT treatment system 110 when kV X-raysource 124 is rotated to a position directly above couch 123 and X-rayimager 150 is positioned below couch 123. As shown, at such a point intime, X-ray imager 150 is in the lateral offset imaging position toenable half-fan CBCT X-ray imaging of thorax 301 of patient 160. Thus,X-ray imager 150 is positioned so that edge 151 and/or edge portion 152of X-ray imager 150 is substantially aligned with longitudinal axis 303of couch 123.

Second combined filter-collimator assembly 240 includes a collimator610, a compensating filter 620, and, in some embodiments, an intensityfilter 630. Collimator 610 is configured to limit the extent of X-rayexposure in lateral direction 311 of patient 160 and to align incidentimaging beam 126 with X-ray imager 150. For example, in someembodiments, collimator 610 includes two blades 601 with an opening 602therebetween that is sized to enable imaging beam 126 to reach most orall of the detector surface of X-ray imager 150 as shown. Blades 601 caneach include a plate formed from similar materials as described abovefor blades 401. Generally, opening 602 is fixed. Compensating filter 620is configured to create a more uniform intensity of imaging beam 126across the surface of X-ray imager 150 when X-ray imager 150 is in thelateral offset imaging position. Compensating filter 620 can be, forexample, a half-bowtie filter, and in some embodiments, can be formedfrom aluminum.

Intensity filter 630 is configured to provide additional X-rayfiltering, and is typically a uniform plate of X-ray absorbing material,such as titanium. In some embodiments, intensity filter 630 isphysically coupled to or mounted on second combined filter-collimatorassembly 240, and therefore is moved together with second combinedfilter-collimator assembly 240 by positioning mechanism 220.Alternatively, intensity filter 630 can be moved into position in X-raypath 202 separately from second combined filter-collimator assembly 240.Similarly, in some embodiments, collimator 610 is physically coupled toor mounted on compensating filter 620, and therefore is moved togetherwith compensating filter 620 as a single assembly by positioningmechanism 220. Alternatively, collimator 610 can be moved into positionin X-ray path 202 separately from compensating filter 620 by positioningmechanism 220. Together, longitudinal collimator 410 and collimator 610define the rectangular region of X-ray imager 150 and patient 160 thatis exposed to imaging beam 126.

As noted above, positioning mechanism 220 can include any suitablemechanism operable to selectively position one of first combinedfilter-collimator assembly 230, second combined filter-collimatorassembly 240, or filter-free collimator 250 along X-ray path 202. FIG. 7schematically illustrates one such embodiment. FIG. 7 is a schematicview from X-ray imager 150 of positioning mechanism 220, first combinedfilter-collimator assembly 230, second combined filter-collimatorassembly 240, and filter-free collimator 250, according to an embodimentof the present disclosure. In the embodiment illustrated in FIG. 7,filter-free collimator 250 is disposed along X-ray path 202, which issubstantially centered in lateral direction 311 between blades 401 offilter-free collimator 250 and in longitudinal direction 312 betweenblades 411 of longitudinal collimator 410. As a result, an X-ray focalpoint 701 of kV X-ray source 124 is located at or near a center point ofthe field of view defined by longitudinal collimator 410 and one offilter-free collimator 250, collimator 510, or collimator 610.

In the embodiment illustrated in FIG. 7, positioning mechanism 220 isconfigured as a lateral direction slider mechanism that translates firstcombined filter-collimator assembly 230, second combinedfilter-collimator assembly 240, and filter-free collimator 250 back andforth in lateral direction 311. Thus, positioning mechanism 220selectively positions a suitable filter-collimator assembly betweenX-ray imager 150 and kV X-ray source 124.

In some embodiments, blades 411 of longitudinal collimator 410 are set afixed distance W apart and are fixed in position relative to positioningmechanism 220. Alternatively, blades 411 can be movable in longitudinaldirection 312 to adjust the X-ray field size and location inlongitudinal direction 312. In such embodiments, blades 411 can beindependently movable, thereby allowing asymmetrical field-sizeadjustments in longitudinal direction 312. Alternatively oradditionally, blades 411 can be mechanically coupled to each other andmoved in conjunction with each other in longitudinal direction 312. Insome embodiments, blades 411 are fixed in position relative to kV X-raysource 124.

In some embodiments, blades 411 are mounted on positioning mechanism220. In such an embodiment, there is generally a different pair ofblades 411 for each position of positioning mechanism 220: one pairassociated with first combined filter-collimator assembly 230, one pairassociated with second combined filter-collimator assembly 240, and onepair associated with filter-free collimator 250. Consequently, in suchembodiments, there can be a different longitudinal field size for eachslider position of positioning mechanism 220.

In some embodiments, positioning mechanism 220 is moved in lateraldirection 311 via a motorized actuator (not shown). Alternatively oradditionally, positioning mechanism can be moved in lateral direction311 manually, or by any other suitable actuation mechanism.

In some embodiments, positioning mechanism 220 is configured totranslate first combined filter-collimator assembly 230, second combinedfilter-collimator assembly 240, and filter-free collimator 250 inlongitudinal direction 312 instead of in lateral direction 311. FIG. 8schematically illustrates one such embodiment. FIG. 8 is a schematicview from X-ray imager 150 of positioning mechanism 220, first combinedfilter-collimator assembly 230, second combined filter-collimatorassembly 240, and filter-free collimator 250, according to an embodimentof the present disclosure. In the embodiment illustrated in FIG. 8,positioning mechanism 220 translates first combined filter-collimatorassembly 230, second combined filter-collimator assembly 240, andfilter-free collimator 250 in longitudinal direction 312. Filter-freecollimator 250 is shown disposed along X-ray path 202 (not shown). As aresult, X-ray focal point 701 of kV X-ray source 124 is located at ornear a center point of the field of view defined by filter-freecollimator 250 and blades 811 of a longitudinal collimator 810associated therewith.

It is noted that when positioning mechanism 220 is configured totranslate longitudinally, a different longitudinal collimator isassociated with each of filter-free collimator 250, first combinedfilter-collimator assembly 230, second combined filter-collimatorassembly 240. For example, in the embodiment illustrated in FIG. 8,longitudinal collimator plates 831 form the top and bottom edges of anopening 832 and perform the function of blades 411 in FIG. 4 for firstcombined filter-collimator assembly 230. Thus, longitudinal collimatorplates 831 define the longitudinal dimension 833 of first combinedfilter-collimator assembly 230. Similarly, longitudinal collimatorplates 841 form the top and bottom edges of an opening 842 and performthe function of blades 411 in FIG. 4 for second combinedfilter-collimator assembly 240. Thus, longitudinal collimator plates 841define the longitudinal dimension 843 of second combinedfilter-collimator assembly 240.

It is further noted that positioning mechanism 220 is generally largerin embodiments in which translation of combined filter-collimatorassemblies is in longitudinal direction 312. However, advantageously, insuch embodiments, positioning accuracy of the longitudinal slidingmotion has less impact on performance of the imaging system when movingthe slider longitudinally.

In other embodiments, positioning mechanism 220 can be configured toselectively rotate one of first combined filter-collimator assembly 230,second combined filter-collimator assembly 240, or filter-freecollimator 250 into X-ray path 202. For example, in one such embodiment,each of first combined filter-collimator assembly 230, second combinedfilter-collimator assembly 240, and filter-free collimator 250 aredisposed in a planar array that is rotated by positioning mechanism 220in a plane parallel to X-ray imager 150.

FIG. 9 sets forth a flowchart summarizing an example method forgenerating an X-ray image, according to one or more embodiments of thepresent disclosure. The method may include one or more operations,functions, or actions as illustrated by one or more of blocks 901-904.Although the blocks are illustrated in a sequential order, these blocksmay be performed in parallel, and/or in a different order than thosedescribed herein. Also, the various blocks may be combined into fewerblocks, divided into additional blocks, and/or eliminated based upon thedesired implementation. Although the method is described in conjunctionwith RT treatment system 110 of FIGS. 1-8, persons skilled in the artwill understand that any suitably configured system is within the scopeof the present disclosure.

In the embodiment described in conjunction with FIG. 9, the controlalgorithms for the method steps reside in and/or are performed by imageacquisition and treatment control computer 131. In other embodiments,such control algorithms may reside in and/or be performed by any othersuitable control circuit or computing device.

A method 900 begins at step 901, in which a first collimator (forexample, collimator 510) is positioned in X-ray path 202 at distance L2from kV X-ray source 124, and a first compensating filter (for example,compensating filter 520) is positioned in X-ray path 202 at distance L4from kV X-ray source 124. The first collimator is configured with afirst opening (for example, opening 502), so that when the firstcollimator is positioned at distance L2 from X-ray imager 150, the firstopening defines a width of a first imaging field, such as the width of apatient head 302 on couch 123 or half the width of a patient thorax 301.In addition, the first collimator is positioned a fixed distance L2-L4from in X-ray path 202 from the first compensating filter. Whenpositioned at the fixed distance L2-L4 in X-ray path 202 from the firstcollimator, the first compensating filter is located so that a photonflux of X-rays from kV X-ray source 124 on X-ray imager 150 is morebalanced than when the first compensating filter is not positioned inthe first imaging field at the distance L2-L4 from the first collimator.

In some embodiments, the first collimator and the first compensatingfilter are positioned in step 901 via a single mechanical operation. Thesingle mechanical operation generally includes one of a lateral slidingmotion, a longitudinal sliding motion, and a planar rotational motion ofthe first collimator and the first compensating filter. In suchembodiments, a positioning mechanism can perform the single mechanicaloperation. In some embodiments, the lateral sliding motion, thelongitudinal sliding motion, or the planar rotational motion alsoincludes the motion of a second collimator out of X-ray path 202. Insuch embodiments, the lateral sliding motion, the longitudinal slidingmotion, or the planar rotational motion may further include motion of acorresponding second compensation filter out of X-ray path 202.Furthermore, in such embodiments, the lateral sliding motion, thelongitudinal sliding motion, or the planar rotational motion of thesecond collimator and/or the corresponding second compensation filtermay be performed simultaneously with the lateral sliding motion,longitudinal sliding motion, or planar rotational motion of the firstcollimator and the first compensating filter.

In step 902, while i) X-ray imager 150 is positioned at a the fixedimaging distance along X-ray path 202 from kV X-ray source 124 of step901, ii) the first collimator is positioned in X-ray path 202 at thefirst fixed distance along X-ray path 202 from kV X-ray source 124, andiii) the first compensating filter is positioned in X-ray path 202 atthe second fixed distance along X-ray path 202 from the firstcollimator, the X-ray source and the X-ray imager are rotated aboutcenter point of rotation 201 to a certain rotational location withrespect to a patient on couch 123.

pow In step 903, while kV X-ray source 124 and X-ray imager 150 arerotated about center point of rotation 201, X-rays generated by kV X-raysource 124 are received with X-ray imager 150, which can then generatean X-ray image.

In step 904, image acquisition and treatment control computer 131determines whether additional X-ray images are to be generated by X-rayimager 150. If yes, method 900 proceeds back to step 902, components ofRT treatment system 110 continue to rotate about patient 160, andadditional X-ray images are generated; if no, method 900 terminates.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments will be apparent to those skilled in the art.The various aspects and embodiments disclosed herein are for purposes ofillustration and are not intended to be limiting, with the true scopeand spirit being indicated by the following claims.

I claim:
 1. An imaging system configured to rotate about a center pointof rotation, the imaging system comprising: an X-ray source configuredto direct X-rays along an X-ray path that passes through the centerpoint of rotation to an X-ray imager; the X-ray imager, which ispositioned at a fixed imaging distance along the X-ray path from theX-ray source and is configured to generate an X-ray image from theX-rays; a first combined filter-collimator assembly that includes afirst collimator configured with a first opening and a firstcompensating filter, wherein the first collimator and the firstcompensating filter are fixed in position relative to each other and thefirst opening is formed by two blades that oppose each other; and apositioning mechanism that is configured to position the first combinedfilter-collimator assembly in the X-ray path so that: the firstcollimator is in the X-ray path at a first fixed distance along theX-ray path from the X-ray source and the first opening defines a widthof a first imaging field; and the first compensating filter is in thefirst imaging field at a second fixed distance along the X-ray path fromthe first collimator.
 2. The imaging system of claim 1, furthercomprising a second combined filter-collimator assembly that includes asecond collimator configured with a second opening and wherein thepositioning mechanism is further configured to: position the firstcollimator and the first compensating filter out of the X-ray path; andposition the second collimator in the X-ray path at a third fixeddistance from the X-ray source along the X-ray path so that the secondopening defines a width of a second imaging field.
 3. The imaging systemof claim 2, wherein the positioning mechanism is configured to positionthe first collimator and the first compensating filter out of the X-raypath and position the second collimator in the X-ray path at the thirdfixed distance with a single mechanical operation.
 4. The imaging systemof claim 3, wherein the single mechanical operation includes a motion ofthe first collimator, the first compensating filter, and the secondcollimator in a direction perpendicular to the X-ray path.
 5. Theimaging system of claim 2, wherein the second combined filter-collimatorassembly further includes a second compensating filter that is fixed inposition relative to the second collimator and the positioning mechanismis further configured to position the second compensating filter in thesecond imaging field at a fourth fixed distance from the secondcollimator along the X-ray path.
 6. The imaging system of claim 2,wherein the X-ray imager is disposed at the fixed imaging distance alongthe X-ray path from the X-ray source when the first collimator ispositioned in the X-ray path at the first fixed distance from the X-raysource and when the second collimator is positioned in the X-ray path atthe third fixed distance from the X-ray source.
 7. The imaging system ofclaim 2, wherein the positioning mechanism is configured tosimultaneously position the first combined filter-collimator assemblyout of the X-ray path and position the second collimator of the secondcombined filter-collimator assembly in the X-ray path at the secondfixed distance.
 8. The imaging system of claim 1, wherein the X-rayimager is configured to: generate images in a first imaging position, inwhich a first portion of the X-ray imager is disposed at the fixedimaging distance along the X-ray path from the X-ray source; andgenerate images in a second imaging position, in which a second portionof the X-ray imager is disposed at the fixed imaging distance along theX-ray path from the X-ray source and the X-ray imager is displaced fromthe first imaging position in a direction perpendicular to the X-raypath.
 9. The imaging system of claim 8, wherein the first portion of theX-ray imager comprises a center point of an X-ray detection surface ofthe X-ray imager and the second portion comprises an edge portion of theX-ray imager.
 10. The imaging system of claim 1, wherein the positioningmechanism is configured to position the first compensating filter in thefirst imaging field at the fixed distance from the first collimatoralong the X-ray path and not at any other distance from the firstcollimator when the first compensating filter is in the first imagingfield.
 11. The imaging system of claim 1, further comprising a secondcollimator that is disposed between the X-ray source and the X-rayimager and includes a second opening that defines a length of the firstimaging field.
 12. The imaging system of claim 11, wherein the secondcollimator includes movable blades that modify the second opening. 13.The imaging system of claim 12, wherein the movable blades areconfigured to change a width of the second opening.
 14. The imagingsystem of claim 12, wherein the movable blades are configured to moveindependently from each other.
 15. The imaging system of claim 12,wherein the movable blades are configured to change a longitudinallocation of the second opening.
 16. A method of generating an X-rayimage in a system that includes an X-ray source and an X-ray imager,wherein the X-ray source is configured to direct X-rays along an X-raypath that passes through a center point of rotation of the system to theX-ray imager and the X-ray imager is configured to generate an X-rayimage from the X-rays, the method comprising: positioning in the X-raypath a combined filter-collimator assembly that includes a firstcollimator configured with a first opening that is formed by two bladesthat oppose each and a first compensating filter, so that the firstcollimator is at a first fixed distance along the X-ray path from theX-ray source and defines a width of a first imaging field and the firstcompensating filter is at a second fixed distance along the X-ray pathfrom the first collimator; while the imager is positioned at a fixedimaging distance along the X-ray path from the X-ray source, the firstcollimator is positioned in the X-ray path at the first fixed distancealong the X-ray path from the X-ray source, and the first compensatingfilter is positioned in the X-ray path at the second fixed distancealong the X-ray path from the first collimator, rotating the X-raysource and the X-ray imager about the center point of rotation; andwhile rotating the X-ray source and the X-ray imager about the centerpoint of rotation, receiving the X-rays with the X-ray imager.
 17. Themethod of claim 16, wherein positioning the combined filter-collimatorassembly so that the first collimator is in the X-ray path at the firstfixed distance and the first compensating filter is in the X-ray path atthe second fixed distance comprises positioning a second collimator outof the X-ray path.
 18. The method of claim 16, wherein positioning thefirst collimator in the X-ray path, positioning the first compensatingfilter in the X-ray path, and positioning second collimator out of theX-ray path is performed via a single mechanical operation.
 19. Themethod of claim 16, wherein the first collimator and the firstcompensating filter are fixed in position relative to each other in thecombined filter-collimator assembly.
 20. The method of claim 16, whereinthe two blades oppose each other in a lateral direction that isperpendicular to the X-ray path and are positioned to limit an extent ofexposure to the X-rays in the lateral direction to no more than thewidth of the X-ray imager.